The present invention pertains to a looper control apparatus for chain-stitch zig-zag sewing machines and more specifically, for making a very wide zig-zag stitch, and for multi-stitch zig-zag. As is well-known, in zig-zag machines the looper travels in an essentially elliptical path while the needle successively travels in two or more parallel, vertical and spaced pathways in order to cover the desired width of the stitch and to cooperate with the looper so as to link the thread of the needle with that of said looper.
When the width of the zig-zag stitch is increased, difficulties arise in the formation of the stitch, due to the fact that the needle is caused to be moved laterally to positions that are of greater distance from the starting point of the looper as said needle moves away from the position in alignment with its initial penetration of the fabric.
This movement of the needle from the position in alignment with its initial penetration of the fabric results in an increase in its lateral movement which increases with the increase in the width of the zig-zag stitch to be covered.
As operation of the looper is determined when the needle is at its point of initial penetration, it is obvious that the constant speed of the looper drive is no longer adequate to compensate for the increase in distance that is present with each successive penetration of the needle during its lateral movements.
Under such conditions it is very likely that the penetrations following those stitches in alignment with the needle's initial penetration will be missed, because the needle and the looper do not meet under the same conditions as those stitches formed in alignment with said needle's initial penetration of the fabric.
In order to obviate the difficulties described above, devices are known which provide for the alternate shifting of the starting point of the looper as the needle moves away from the stitches in alignment with its initial penetration. In order to accomplish this, the pin around which the looper support oscillates is shifted in the same direction and distance as the needle.
This device, however, has a disadvantage, owing to the different position of the looper from that of the needle relative to the successive penetrations of the latter. This is due to the different angles that the looper assumes according to the repeated positions assumed by the above-mentioned pin. This, in turn, is due to the fact that the pin on which the looper drive shaft pivots does not move in correspondence with the pin on which the looper support oscillates.
The present invention proposes to obviate the difficulties mentioned above and provide the desired form of zig-zag chain stitch irrespective of the width of the stitch and the number of penetrations per lateral movement in both directions of the needle.
The problem has been solved by providing a means which causes the looper to assume positions which provide the same operative association between it and the needle with each successive penetration and position of the latter.